The present invention relates to automatic frequency response control of a filter, and more particularly, to a filter having a bell shaped response such as is used in a SECAM TV camera encoder.
Recent developments concerning the French SECAM standard indicate that several tolerances of the SECAM system will be made much tighter in the future. This not only leads to problems in designing encoder circuits, but also makes it difficult to adjust SECAM encoders in the production line. Test equipment such as vectorscopes, which allow simple and precision adjustment of NTSC or PAL encoders, do not exist for SECAM. Therefore it is very desirable to introduce self-adjusting circuits in SECAM encoders.
One of the circuits used in a SECAM encoder is a notch filter having a bell shaped amplitude frequency response. This filter must have a stable frequency characteristic for proper encoding to take place. Unfortunately, the components comprising the filter have values that change with time, thus requiring periodic readjustment of the filter.